(Reuters) – Hundreds of armed men descended on a village in northern Thailand and overpowered residents blocking the road to a goldmine said by locals to have caused environmental damage so that trucks could take ore away, villagers said on Friday.

Wearing black and white ski masks and armed with guns, knives and clubs, up to 400 men rounded up and beat 40 people, including women, in the Khao Luang district of Loei province near the northern border with Laos.

Environmental activist group Ecological Alert and Recovery – Thailand (EARTH) said at least 20 people were injured in the attack on Thursday. The unidentified assailants left on Friday.

“They covered villagers’ eyes, bound their ankles and wrists and beat them black and blue. They treated us like we weren’t human,” one villager, Pauntip Hongchai, told Reuters by phone.

Residents of Khao Luang have for years contested the mining operations of Tungkum Ltd, a subsidiary of Tongkah Harbour Pcl.

Villagers and activists say Tungkum has poisoned the creeks and waterways on which the communities rely for irrigation and food. Many people have fallen ill, said Nicha Rakpanichmanee, a research officer with EARTH.

“After years of complaints and no action from any government agency to stop the contamination – and villagers felt the contamination was getting worse – the villagers set up a blockade late last year to block large trucks from entering or leaving the premises,” she said by phone.

The attackers used a company tractor to destroy the barricade and then moved 13 trucks carrying ore out of the village, residents said.

“People are ill,” said Wiraun Rujichaiwat, whose husband was among those beaten. “There are chemicals in the food we grow around our homes. We don’t want them mining here. We’re against them, and we want them to stop.”